The Family Nitrospiraceae

Nitrospiraceae is the only established family in the phylum Nitrospirae and comprises the genera Nitrospira, Leptospirillum, and Thermodesulfovibrio. In phylogenetic trees based on 16S rRNA gene sequences Nitrospira and Leptospirillum consistently cluster together, whereas Thermodesulfovibrio forms a separate branch within the phylum. The family is physiologically highly diverse and contains chemolithoautotrophic aerobic nitrite-oxidizing bacteria (Nitrospira), chemolithoautotrophic aerobic and acidophilic ferrous iron oxidizers (Leptospirillum), and anaerobic, thermophilic, chemoorganoheterotrophic or hydrogenotrophic sulfate reducers (Thermodesulfovibrio). Members of the family occur in a wide range of natural and man-made ecosystems. In particular, the genus Nitrospira is almost ubiquitously distributed in oxic habitats and represents the predominant known nitrite oxidizers in nature, which catalyze the second step of nitrification and thus are essential for biogeochemical nitrogen cycling. All three genera are relevant for biotechnological processes. The genus Nitrospira contains the key nitrite oxidizers in biological wastewater treatment plants, whereas members of Leptospirillum are important iron oxidizers in the bioleaching of metal ores and are involved in acid mine drainage. Thermodesulfovibrio representatives occur in anaerobic digesters, where they contribute to the degradation of organic compounds and indirectly to the production of methane. Especially the members of Nitrospira and Leptospirillum are difficult to cultivate and most of their diversity has been detected by cultivation-independent molecular approaches.